Detecting an object by means of light source measurement typically causes many problems, because different objects reflect light with different power intensity [W/m2]. This is the result of different objects having a different reflection coefficient. In practice, variation can be detected by the human eye such that different objects display in different colours. When using light source measurement, the position of the object can be determined by means of the power intensity reflected by the object.
Many techniques exist by means of which the object can be detected even though its reflection coefficient is unknown when performing the measurement. One of the known techniques is position sensitive measurement which is also known by the term position sensitive device (PSD). Usually, the PSD device comprises a light signal source and a signal receiver. When said light source emits light signals and light rays meet the object, at least part of said light signals are reflected back and meet the surface of the PSD receiver. The receiver does not conduct electricity in usual conditions, but the reflected light rays include photons which can release carrier particles in the PSD receiver and induce several electric currents in the PSD receiver. By measuring the position of the induced electric currents in the PSD receiver, the position of the object can be determined.
By means of this method comparing the position of electric currents, the position of the object can be determined even though the reflection coefficient of the object is unknown. The PSD device comprises various details related to microelectronics. Furthermore, said apparatus requires several amplifiers. Due to these issues, PSDs are too expensive for use in all such applications in which the aim is to detect an object.
Another technique for detecting an object is known. This technique utilises a light source and at least two separate receivers which are on the same plane with said light source. Into connection with each receiver is arranged at least one amplifier. When said light source emits light and light rays meet the object, at least part of said light signals are reflected back and meet the surface of one receiver. The angle between the transmitted light signal and the reflected light signal varies depending on the position of the object in relation to the light source and this has an effect on which receiver receives the reflected light signal. In the case of the object having been in some other position, at least part of the light signals would also in this case be reflected back and the angle between the transmitted light signal and the reflected light signal would have been some other. Due to this, the reflected light signal would meet the surface of another receiver.
Either in this arrangement, it is not necessary to know the reflection coefficient of the object in order to determine the position of the object. However, a problem of this arrangement is that it requires several receivers and amplifiers arranged into connection with them and this incurs extra costs for component manufacturers. Furthermore, the amplifiers have to be set in a predetermined position in order to guarantee the operation of said system. Therefore, the device requires a lot of space.
An additional known technique for detecting an object is an apparatus which includes several signal sources for transmitting signals and at least one receiver arranged to receive signals. The propagation directions of signals provided by the signal sources are parallel in relation to each other. When said object is in the propagation direction of these signals, at least part of said signals are reflected in the receiver which receives said signals. A problem of this known arrangement is that the difference in the power intensity of received signals is small, because the propagation paths of the signals are parallel in relation to each other. Due to this, several amplifiers are required and this increases the manufacturing costs of this known technique.